Due to the increasing number of silent consumers such as the IR receiver of the central locking system, anti-theft device, sensors, etc., vehicles have substantial power consumption, even when shut off. There is the risk that a shut-off vehicle may no longer be able to be started after a prolonged standstill. Therefore, devices indicating the starting ability are used to inform the driver.
A device for predicting the starting ability of a vehicle indicates how long a vehicle may be shut off until the vehicle battery is discharged to a point that the vehicle is just able to be restarted or whether a start is still possible after a predefined time has elapsed. The starting ability of a vehicle is normally assumed when the battery is able to provide a predefined electric starting power without falling short of a set minimum terminal voltage.
German Patent Application No. DE 197 05 634, for example, describes determining the starting ability of a vehicle at a predefined starting current and a given starting temperature by calculating the terminal voltage of the battery during a starting operation. The terminal voltage is calculated from the no-load voltage and the internal resistance of the starter battery. The starting current is measured during the starting operation. A prediction about a future starting ability of a vehicle is not possible. In addition, it is relatively complex to measure the starting current of the battery during a starting operation.
A method for determining the starting ability of a vehicle is described in German Patent Application No. DE 1056970 in which an average voltage drop in the battery is calculated during a starting phase and it is determined whether or not a minimum terminal voltage of the battery was not met. This method also places high demands on the sensor for measuring the battery voltage and additionally requires constant calculation of the battery behavior during a starting operation. Moreover, a prediction about the future starting ability of a vehicle is not possible.